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Answer:
a = √(b² +c² -2bc·cos(A))
a = √(c² -b²)
Step-by-step explanation:
For sides a, b, c, and opposite angles A, B, C, the general form of the law of cosines is ...
a² = b² + c² -2bc·cos(A)
An expression for 'a' can be written by taking the square root.
a = √(b² +c² -2bc·cos(A))
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If you recognize that cos(A) = b/c, then a substitution can be made:
a = √(b² +c² -2(bc)(b/c)) = √(b² +c² -2b²)
a = √(c² -b²) . . . . . . . same as the Pythagorean theorem
